VC10LPFilter

V = Variables

C = Calculation functions

The VC10LPFilter function implements a first-order low-pass digital filter (RC filter) for WORD dimension data.

IMPLEMENTATION

VC10LPFilter (Tsample, Tau, FilterIn, FilterOut)

Parameters:

IN/OUT	VARIABLE TYPE	EXAMPLE NAME	DIM
IN	SYSTEM	swTsample	W	Sample time filter (msec) [0÷32767].
IN	SYSTEM	swTau	W	The filter time constant (ms) [0÷32767]
IN	GLOBAL	gwFilterIn	W	Value of the variable that you want to filter (UM) [-32768÷32767]
OUT	GLOBAL	gwFilterOut	W	Value of the filtered variable (UM) [-32768÷32767]

Description

The VC10LPFilter function implements a digital low-pass filter of the first order whose time constant (Tau) is defined in the parameters passed to the function itself. Assuming you start from a zero input variable value the output of the filter takes a value equal to 63% of the entrance after the long Tau time. Similarly the cutoff frequency of the filter is

Example

;---------------------------------------------
; Project           : REG_012
; Module Name  : ReadTemp
; Author            : 
; Description     : Read temperature & filter
;---------------------------------------------
MAIN:
	CALL ReadTemp
	swTsample = 100		;100 ms sampling time filter
        swTau = 5000		;5 sec filter time constant
	VC10LPFilter (swTsample, swTau, gwFilterIn, gwFilterOut)
 
WAIT 1
JUMP MAIN

Note

La funzione contiene un timer che scandisce il tempo di campionamento del filtro. E' importante quindi che la funzione venga posto del software che viene eseguito ad ogni ciclo task.